Title: Molecular-Scale Understanding of Sulfate Exchange from Schwertmannite by Chromate Versus Arsenate

Abstract

Schwertmannite effectively sorbs chromate (Cr(VI)), yet the sorption mechanisms remain elusive. We determined the Cr(VI) sorption mechanisms on schwertmannite at pH 3.2 and 5 using combined macroscopic sorption experiments with molecularscale characterization and by comparing them to arsenate (As(V)) sorption. Cr(VI) adsorbs as bidentate-binuclear (BB) inner-sphere complexes through exchanging more sulfate and less >Fe–OH/OH₂, with 0.59–0.71 sulfate released per Cr(VI) sorbed. While As(V) also forms BB complexes, it exchanges sulfate and >Fe–OH/OH₂ equally with 0.49–0.52 sulfate released per As(V) sorbed. At high As(V) loadings, As(V) precipitates as amorphous FeAsO₄, particularly at low pH. The abovementioned differences between Cr(VI) and As(V) can be related to their different ionic radii and binding strength. Moreover, Cr(VI) and As(V) preferentially exchange sulfate innersphere complexes, increasing the proportion of sulfate outer-sphere complexes in schwertmannite. In turn, the concentration of sulfate outer-sphere complexes increases and then decreases with increasing Cr(VI) loading. Results suggest that an oxyanion, which would form inner-sphere complexes on a mineral surface, preferentially exchanges inner-spherically bound oxyanions than outerspherically bound ones on the surface, even though both are exchanged. Furthermore, this study improves our understanding of the sorption of oxyanions on schwertmannite and their capabilities to template schwertmannite formation and stabilize its structure.

Authors:

Wang, Xiaoming  ^[1];

• Search DOE PAGES for author "Wang, Xiaoming"
• Search DOE PAGES for ORCID "0000-0002-5484-3922"

Ying, Hong ^[2]; Zhao, Wantong ^[2]; Feng, Xionghan  ^[2];

• Search DOE PAGES for author "Feng, Xionghan"
• Search DOE PAGES for ORCID "0000-0001-5499-7174"

Tan, Wenfeng ^[2]; Beyer, Kevin A. ^[3]; Huang, Qiaoyun  ^[2];

• Search DOE PAGES for author "Huang, Qiaoyun"
• Search DOE PAGES for ORCID "0000-0002-2733-8066"

Liu, Fan  ^[2];

• Search DOE PAGES for author "Liu, Fan"
• Search DOE PAGES for ORCID "0000-0003-0341-923X"

Zhu, Mengqiang  ^[4]

• Search DOE PAGES for author "Zhu, Mengqiang"
• Search DOE PAGES for ORCID "0000-0003-1739-1055"

---

+ Show Author Affiliations

1. Huazhong Agricultural Univ., Wuhan (China); Univ. of Wyoming, Laramie, WY (United States)
2. Huazhong Agricultural Univ., Wuhan (China)
3. Argonne National Lab. (ANL), Lemont, IL (United States)
4. Univ. of Wyoming, Laramie, WY (United States)

Publication Date:

Wed Apr 07 00:00:00 EDT 2021

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Wyoming, Laramie, WY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Natural Science Foundation of China (NSFC); Fundamental Research Funds for the Central Universities; National Science Foundation (NSF)

OSTI Identifier:

1819669

Alternate Identifier(s):

OSTI ID: 1854158

Grant/Contract Number:  

AC02-06CH11357; AC02-76SF00515; SC0016272

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Science and Technology

Additional Journal Information:

Journal Volume: 55; Journal Issue: 9; Journal ID: ISSN 0013-936X

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Schwertmannite; arsenate; chromate; inner-sphere complex; outer-sphere complex; precipitation; preferentially exchange; sulfate; sorption; oxides; anions; adsorption; extended x-ray absorption fine structure; 58 GEOSCIENCES